A honeycomb structure is installed into a gas exhaust system of a diesel engine to be used as a trapping filter for exhaust gas, for example, as a diesel particulate filter (DPF) for trapping and removing particulate matter contained in exhaust gas from a diesel engine or the like. Such a honeycomb structure has an weakness of having a defect such as a crack due to thermal stress generated in accordance with a difference in thermal expansion depending on a portion because of uneven temperature rise depending on a portion derived from an uneven gas flow, or the like, upon use (upon trapping and removing particulate matter) and upon regeneration (upon combusting and removing particulate matter accumulated inside the filter in order to eliminate increase in pressure loss due to particulate matter accumulated inside the filter in the course of time).
By considering that, in particular, a honeycomb structure using silicon carbide (SiC) as a part of raw material has a large thermal expansion coefficient (a high thermal stress generation) in comparison with a cordierite honeycomb structure and low thermal shock resistance though it is excellent in heat resistance, there have been proposed a honeycomb structure having a plurality of honeycomb segments integrally joined at joint faces by means of a bonding material layer to form a honeycomb segment joined body in order to reduce influence of thermal stress, a honeycomb structure where at least one of honeycomb segments not constituting the outermost peripheral surface of the honeycomb structure has a higher average wall thickness and a lower or the same cell density than or as at least one of honeycomb segments constituting the outermost peripheral surface of the honeycomb structure (see Patent Document 1), a honeycomb structure containing a honeycomb segment having a higher heat capacity per unit volume in the outer peripheral side portion of the honeycomb segment than that in the central side portion of the honeycomb segment (see Patent Document 2), and a honeycomb filter having a higher heat capacity in the central portion in a cross-section perpendicular to an axial direction of the honeycomb filter than that in the peripheral portion in the cross-section (see Patent Document 3). However, it is difficult to solve a local temperature rise of a honeycomb structure according to local and drastic heat generation only by measures related to heat capacity, and the aforementioned inconvenience cannot always be inhibited sufficiently. In particular, as a filter has recently been enlarged, thermal stress generated upon use or upon regeneration has remarkably been increased in comparison with a conventional filter, and thereby frequency and extent of occurrence of a defect such as a crack has escalated to a serious state.
Patent Document 1: JP-A-2002-301325
Patent Document 2: JP-A-2003-10616
Patent Document 3: JP-A-2003-254034